1. Field of the Invention
This invention relates to a method for storing a heated asphalt mixture, and more particularly to a method for storing a heated mixture of asphalt such as straight asphalt, semiblown asphalt, blown asphalt, natural asphalt and their mixtures.
2. Description of the Prior Art
Hitherto, it has been a common practice to store heated asphalt mixture in a container under atmospheric pressure. However, such a method suffers from deterioration of the asphalt, because of its contact with oxygen contained in the atmosphere and the decrease in temperature of the asphalt. (Meant by the term, "asphalt" as used herein are straight asphalt, semiblown asphalt, blown asphalt, natural asphalt and their mixtures.) More particularly, it was proved that the penetration degree of asphalt recovered from the mixture after it has been stored for 12 hours was lowered to as low as about 50%, as compared with that of the asphalt recovered immediately after mixing, and that the viscosity of the former was increased to a considerable degree, thereby presenting a deteriorated asphalt mixture which could no longer be used. For this reason, it has been customary that the asphalt is stored only for periods of about several hours. In this case, however, attempts have been proposed to provide a heating device for an asphalt-storing container to prevent the decrease in temperature of a heated asphalt mixture. However, this attempt only meets with partial success, still suffering from the deterioration such as lowering in penetration degree and extreme increase in viscosity of asphalt due to its contact with oxygen contained in the atmosphere. In other words, the storage of asphalt results in the deterioration such as extreme decrease in penetration degree of asphalt contained in the mixture, and thus the asphalt will no longer be useful after a short period of time, as has been described so that an attempt to heat an asphalt mixture in storage presents no real improvement in this aspect of the aforesaid shortcomings. As a result, only a heat retaining or insulating device is used for the aforesaid purpose.
Due to the shortcomings experienced with a heated asphalt mixture, if the construction is interrupted due to rail fall or troubles such as in a paving machine and the like, or in case an excessive asphalt mixture results for some reason or other during the construction, or otherwise in case such an excessive asphalt mixture has to be stored for over 12 hours, say for a relatively long period of time including an off-day, then the stored asphalt mixture has to be discarded. There has been another unfavorable aspect of the stored asphalt mixture in that, due to the strict regulation for the night-time operation of a heated asphalt-mixture mixing machine, the heated asphalt mixture which has been mixed during day time has to be thrown away and hence can not be stored over a night, due to the aforesaid deterioration, thus hindering the satisfactory progress of the construction to a great extent.